Hey guys, I have a 2001 suburban that has 107000 miles and has started to have a problem. It seems to idle too high randomly when my wife is out and about. I have seen it a few times and she says it happens regularly. What do you think? It was paid for in June and we plan to keep it for a few years.

Thanks,
Kerry

 

To start with,I'd probably pull of the idle speed motor (AIS, IAC,) or whatever abbreviation your manufacturer uses for it. Either/or, it controls idle up when engine under load, for example , turning, braking, A/C on etc. to allow engine to remain at certain idle speed. The plunger & seat get gummed up & cause similar symptoms like you are describing. Take it off & clean with throttle body cleaner on the plunger of the valve itself & the seat on the throttle body where you removed it from.Usually located on side of throttle body. Give the inside of throttle body a cleaning while your at it.

 

I'm thinking the throttle positon sensor voltage is not returning to what it should have when the throttle is released. It might not be something you can diag yourself with out a scan tool, or a volt meter. I think it's the gray wire, try back probing it with a safety pin and connect a voltmeter to it. Should be around .6-.7 volts at idle. If when it's idling high the voltage hangs around a couple volts, you've found the problem. The idle control systems on those things were not necessarily known for giving trouble......

 

So far so good! Thanks guys.

 

Another way to test your TP sensor (potentiometer) is to remove wire connector from it, touch probes of multimeter on 2 of the pins (trial & error to find which 2 won't hurt anything) on the TP sensor, while meter set on Ohms. (resistance) With engine off, Moving throttle from idle to wide open, slowly should cause meter reading to increase/decrease in conjunction with throttle movement. Move it back & forth slowly & watch meter for a sudden drop or rise along the way. Sudden drop or rise in reading,around same spot, indicates a badspot in the TP sensor.

 

Vacuum leak from the intake gaskets could be the cause, known problem. GM revised the intake gaskets.

 

True enough, didnt know about revised gaskets but, sure is a possibility too.